Main Breaker Panelboards - load side of xfmr

[DW98]

I've posted a similar topic about secondary overcurrent protection for transformers, but have a new related topic. More than once in field surveys, I've come across 208/120Y panelboards on the load side of transformers that are main lugs only, not main breaker. This would mean the panelboard is protected by the circuit breaker protectin the transformer primary. In my opinion, this is a code violation.

Looking for others opinions or experiences with this.

 

[charlie b]

Agreed. That is a violation. You can sometimes protect the secondary windings of a transformer using an OCPD on the primary side. In very limited (and not often encountered) circumstances (that do not include your example), the primary OCPD can also protect the secondary conductors (i.e., the ones leading away from the transformer). However, most often the secondary conductors require overcurrent protection either at the secondary itself, or at their other end, as allowed by 240.21(C). Per 408.36, the panel must be protected against overcurrent "on its supply side." The wording does not allow the protection to be on the supply side of the transformer's supply side.

 

[pete m.]

Per 408.36, the panel must be protected against overcurrent "on its supply side." The wording does not allow the protection to be on the supply side of the transformer's supply side.

I am not following the logic here. It would seem that 408.36(B)exc. would allow it. Did I misunderstand what you have said?


408.36 Overcurrent Protection. In addition to the re-
quirement of 408.30, a panelboard shall be protected by an
overcurrent protective device having a rating not greater
than that of the panelboard. This overcurrent protective de-
vice shall be located within or at any point on the supply
side of the panelboard.
(B) Supplied Through a Transformer. Where a panelboard
is supplied through a transformer, the overcurrent protection
required by 408.36 shall be located on the secondary side of
the transformer.
Exception: A panelboard supplied by the secondary side
of a transformer shall be considered as protected by the
overcurrent protection provided on the primary side of the
transformer where that protection is in accordance with
240.21(C)(1).

Pete

 

[charlie b]

I wasn't clear enough, I find. I did say that protection on the primary side does not apply to the installation under discussion. The key is here:

Exception: A panelboard supplied by the secondary side of a transformer shall be considered as protected by the overcurrent protection provided on the primary side of the transformer where that protection is in accordance with 240.21(C)(1).

That article does not allow primary-side protection for a three phase, delta-wye transformer, such as the 208/102Y under discussion here.

 

[pete m.]

I wasn't clear enough, I find. I did say that protection on the primary side does not apply to the installation under discussion. The key is here:That article does not allow primary-side protection for a three phase, delta-wye transformer, such as the 208/102Y under discussion here.

I appreciate the clarification.

Pete

 

[DW98]

I'm guessing 240.21(C)(1) is not being read close enough, or maybe it's a practice that's been repeated but never caught by plan reviewers and therefore not corrected.

Thank you all for you input. I find this forum very helpful and informative.

 

[infinity]

I've seen this many times in the field. Isn't this secondary conductor protection like engineering 101? I;m wondering how this could this be missed?

 

[dana1028]

I've seen this many times in the field. Isn't this secondary conductor protection like engineering 101? I;m wondering how this could this be missed?

Actually it is VERY easy to miss - I am giving a biased opinion here - depending on where you are in the U.S., MANY regions are using 'Combination' building inspectors [i.e. an inspector who is supposed to be knowledgeable on ALL the codes....bldg, elect, mech, plumbing, Green codes, Energy codes, existing bldg. codes, storm water codes, etc.]. We're talking well over 5,000 pgs. of code language.

Unless the (Combination) inspector in question has a strong electrical background, he is typically lacking knowledge of much more than the very basic [read NM cable] requirements. When you start getting into grounding/bonding/transformers, you are WAY over their level of understanding. They frequently don't have a clue to what they are looking at so it is impossible for them to correct a wrong installation.

 

[infinity]

Actually it is VERY easy to miss - I am giving a biased opinion here - depending on where you are in the U.S., MANY regions are using 'Combination' building inspectors [i.e. an inspector who is supposed to be knowledgeable on ALL the codes....bldg, elect, mech, plumbing, Green codes, Energy codes, existing bldg. codes, storm water codes, etc.]. We're talking well over 5,000 pgs. of code language.

Unless the (Combination) inspector in question has a strong electrical background, he is typically lacking knowledge of much more than the very basic [read NM cable] requirements. When you start getting into grounding/bonding/transformers, you are WAY over their level of understanding. They frequently don't have a clue to what they are looking at so it is impossible for them to correct a wrong installation.

I didn't mean by the inspector I meant by the engineer designing these things. I've seen transformers installed with MLO panels on the secondary many times. Seems that between design, plan review and installation someone should catch this.

 

[dana1028]

I didn't mean by the inspector I meant by the engineer designing these things. I've seen transformers installed with MLO panels on the secondary many times. Seems that between design, plan review and installation someone should catch this.

Got it - however....as 101 as it should be for the engineer and then the alleged qualified commercial electrician - my experience is it just doesn't happen that way.

Quite frequently no one looks at the plans - I often see where the plans are actually correct but no one looked at them [electrician/inspector]. The electrician often 'knows' what the customer wants and puts it together the way he was taught by someone else who 'knew' what they were doing. [Or knew what they were doing 20 yrs. ago - which was the last time they looked in a code book or took a code class].

This is true of even the largest commercial electrical contractors - the strong [or weak] link in the project is the supervising electrician. But frequently these commercial projects go to the low bidder [the weak link].